1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display panel using three electrodes, and a driving method thereof.
2. Discussion of the Related Art
A liquid crystal display device controls the light transmittance of a liquid crystal having a dielectric anisotropy using an electric field, thereby displaying a picture. The liquid crystal display device includes a liquid crystal display panel that displays a picture through a liquid crystal cell matrix, and a drive circuit for driving the liquid crystal display panel.
Referring to FIG. 1, a liquid crystal display panel of the related art includes a color filter substrate 10 bonded to a thin film transistor substrate 20 with a liquid crystal 24 therebetween.
The color filter substrate 10 includes a black matrix 4, a color filter 6 and a common electrode 8 that are sequentially formed on an upper glass substrate 2. The black matrix 4 is formed in a matrix shape on the upper glass substrate 2. The black matrix 4 divides the area of the upper glass substrate 2 into a plurality of cell areas where a color filter 6 is to be formed, and prevents light interference between adjacent cells and external light reflection. The color filter 6 is formed to be divided into red R, green G and blue B in the cell area by the black matrix 4, to transmit red, green, and blue light. The common electrode 8 supplies a common voltage Vcom, which is a standard when driving a liquid crystal 24, to a transparent conductive layer over the entire surface of the color filter 6. And, an overcoat layer (not shown) may be further formed between the color filter 6 and the common electrode 8 in order to level the color filter 6.
The thin film transistor substrate 20 includes a thin film transistor 18 and a pixel electrode 22 which are formed at each cell area defined by the crossing of a gate line 14 and a data line 12 on a lower glass substrate 12. The thin film transistor 18 supplies a data signal from the data line 16 to the pixel electrode 22 in response to a gate signal from the gate line 12. The pixel electrode 22 formed of a transparent conductive layer drives the liquid crystal according to the data signal from the thin film transistor 18.
The liquid crystal 24 having a dielectric anisotropy rotates in accordance with an electric field formed by the data signal on the pixel electrode 22 and the common voltage Vcom on the common electrode 8 to control the light transmittance, thereby realizing a gray level.
The liquid crystal display panel further includes a spacer (not shown) to fix a cell gap between the color filter substrate 10 and the thin film transistor substrate 20.
The related art liquid crystal display panel is an active matrix type because a thin film transistor acting as a device is formed at each liquid crystal cell; thus it is suitable to display motion picture. The related art liquid crystal display panel has a disadvantage in that a motion blurring phenomenon occurs because of a slow response speed caused by the viscosity and elasticity of the liquid crystal.
Accordingly, a three electrode liquid crystal display panel has been recently proposed that may improve the response speed by forming an electric field in horizontal or vertical direction by applying different voltages to three electrodes, i.e., the common electrode and the first and second pixel electrodes. In the three electrode liquid crystal display panel, the liquid crystal cell where the horizontal electric field is formed by the three electrodes displays white, and the liquid crystal cell where the vertical electric field is formed displays black, thus the white and black gray levels are all determined by the electric field applied to the liquid crystal cell. Accordingly, the response speed may be improved in comparison with the existing liquid crystal display panel where the liquid crystal is restored to an initial alignment state when there is no electric field.
However, the three electrode liquid crystal display panel should drive the liquid crystal with alternating current (AC) in order to prevent the liquid crystal from deteriorating, but the AC driving method has not yet been proposed. Accordingly, a specific driving method for AC-driving the three electrode liquid crystal display panel and a three electrode structure which is suitable for AC-driving is required.